Deficit irrigation combined with reduced N-fertilizer rate can mitigate the high nitrous oxide emissions from Chinese drip-fertigated maize field

Agricultural soils are major sources of the greenhouse gas N2O, particularly under maize with high nitrogen (N) inputs and excessive irrigation. To determine how N and water management can mitigate N2O emissions from drip-irrigated maize fields, a field study was carried out in the North China Plain during the maize growing season. The objective of the study was to investigate the individual and combined effects of irrigation level and N input on N2O emissions and grain yields, as well as N and water use efficiency (WUE), under drip-fertigation management. The main treatments were two irrigation levels: 50 mm/event (sufficient irrigation, W-H) and 25 mm/event (limited irrigation, W-L), with four N application rates: 0 (N-0), 90 (N-1), 180 (N-2), and 270 (N-3) kg N ha(-1). Pulses of N2O emissions were recorded every 2-3 d following each irrigation or fertigation (irrigation + fertilization) event. N input, irrigation, and their interactions all significantly influenced N2O emissions. A significant exponential relationship (P < 0.05) was observed between N application rate and cumulative and yield-scaled N2O emissions in both irrigation treatments. The cumulative N2O emission fluxes from the N-0, N-1, N-2, and N-3 levels of fertilizer with W-L were 11.4, 13.8, 27.2, and 58.8% lower, respectively, than those from the same N levels with W-H; this occurred because high pulses of N2O were avoided during low irrigation conditions. Under W-H, denitrification was the likely source of the high amounts of N2O, whereas nitrification was likely the main source of N2O emissions under W-L. The variations in the water-filled pore space (WFPS) between the two irrigation treatments may explain these results. The effect of N fertilizer on grain yield and WUE depended on the availability of soil water. Based on the available soil water content, the regulation of N fertilizer application can increase yield and also reduce cumulative and yield-scaled N2O emissions. (c) 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).